1. Field of the Invention
Apparatuses and methods consistent with the present invention relate to driving a light source, and more particularly, to an apparatus and a method for driving light sources of alternating current (AC) pulse waveforms of different specifications, and a display apparatus using the same.
2. Description of the Related Art
A liquid crystal display (LCD) is a flat-panel display that uses liquid crystal. LCDs are used in many industries due to their advantages such as relatively thinner products, and lower requirements for power consumption and driving voltage.
Because liquid crystal used in a display panel is non-radiant element, the LCD requires a separate light source to emit a light of a predetermined brightness.
A cold cathode fluorescent lamp (CCFL) having a straight glass tube form, has been widely used as a light source. CCFL light sources are mainly classified into an edge light type and a direct light type, according to locations where the light sources are placed.
An edge type light source uses a transparent light guide panel, in which the light source is placed beside the light guide panel such that the light from the light source is multi-reflected against one side of the light guide panel and falls onto the LCD panel. The direct type light source uses a plurality of light sources disposed immediately below the LCD panel, with a diffusing plate provided on the front side of the light source and a reflective plane provided on the rear side of the light source, such that the light from the light source is reflected and diffused before falling onto the LCD panel.
However, the LCD usually has a considerable amount of light loss due to the presence of optical elements such as light guide plate, diffusing plate, or the like, and also has shortcomings of high manufacture cost due to complex structure, and degradation of brightness uniformity.
A surface light source device has recently been developed as a solution to the problems mentioned above. The surface light source device includes a light source having a radiation area, and electrodes to supply radiation voltage to the light source. The surface light source device generates plasma radiation in the radiation area, using the supplied radiation voltage, and emits a ray of light.
The surface light source device includes a radiation gas which is filled in the radiation area, and a first and second electrodes for receiving radiation voltage to form a radiation area and generate plasma radiation. Because the surface light source device requires a predetermined level of capacitance, alternating current (AC) power such as sine wave, is required as radiating voltage.
Examples of a method or a circuit to provide AC power to the surface light source device have been disclosed in U.S. Patent Application Publication No. 2007/0018590, Korean Patent No. 10-0467875, and Japanese Patent No. 2006-338897.
Factors that determine driving efficiency of the surface light source device include pulse form and pulsewidth of the AC power which is separated during a pause. The general duty ratio of the pulse ranges from 1:5 to 1:10.
However, most of the previously suggested techniques considered only one factor to determine the driving efficiency, in which either the monopole pulse separated during a pause is provided, without considering the time required for the charging or discharging of the capacitor, or bipolar pulse is provided without considering the pause.
Accordingly, when the related art apparatuses or methods as the ones disclosed in the abovementioned publications are applied, lifespan of the light source is shortened due to use of monopole pulse and subsequent generation of bias stress. Furthermore, on a designing part, it is hard to ensure a sufficient length of pause to achieve the desired light source driving efficiency.
Furthermore, due to a requirement of a boost converter to provide light source driving efficiency, and sufficient level of AC power, product size and manufacture cost increase.
Furthermore, because AC power of a fixed pulsewidth or a fixed length of pause is supplied to the light source, an apparatus or a method is required, which is capable of providing a customized pulsewidth and length of pause according to the types of radiating gases, and thus achieving maximum light source driving efficiency.